Magnetic loop antennas have a number of applications, including incorporation as parts of transmitting and receiving systems for communications, and are particularly applicable to methods of communication underwater using electromagnetic and/or magneto-inductive means. Because water, especially seawater, is partially conductive, relatively low signal frequencies are commonly employed in communication systems underwater in order to reduce signal attenuation as much as possible. To this end, antennas in most applications are generally formed of conducting loops.
In a loop antenna forming part of a transmitter system it can be advantageous to increase current in the transmit loop so that the magnetic moment (or field strength) of the resultant transmitted electromagnetic signal is increased. Because a coiled transmit loop exhibits inductance, one way of achieving this is to make the transmit loop the inductive component of an electrically resonant tuned circuit. The other complementary component required to achieve resonance may conveniently be a capacitor connected in series with the inductive loop.
Similarly, it can be advantageous in a loop antenna used as part of a receiver system to maximise the voltage created across the output terminals of a receive loop antenna thereby optimising the signal passed to following receive circuits for detection and processing. In comparable alternative designs, receive signal current may be maximised. In either case, this also can be achieved by making the loop the inductive component of an electrically resonant tuned circuit. A capacitor connected in series with the inductive loop will act to maximise loop current while a parallel-connected capacitor maximises voltage induced across the resonant circuit.